The oxygen reduction reaction activity and selectivity of porous-carbon supported transition metals (M-C: M Mn, Fe, Co, Ni, Cu) electrocatalysts

Abstract

In general, both transition metal addition and nitrogen doping are important to the four-electron (4e−) oxygen reduction reaction (ORR) activity of carbon-based catalysts, in which nitrogen-containing species, such as M-Nx, pyridinic N and graphitic N, are believed to be the active sites. On the other hand, nitrogen-free carbon supported transition metals often show their excellent electroactivity toward two-electron (2e−) ORR. Herein, carbon supported transition metal catalysts (M-C: MMn, Fe, Co, Ni, Cu) with high specific surface areas were prepared by a simple zinc-mediated pyrolysis method and their ORR activity and selectivity were systematically studied. It is found that various transition metals result in a large difference in the content and type of oxygen-containing functional groups of the M-C catalysts. The results show that CuC and CoC exhibit promising ORR activity close to the 4e− transfer mechanism in 0.1 M KOH electrolyte. FeC and MnC show a mixture of 2e− and 4e− transfer pathways. NiC is an efficient catalyst for efficient H2O2 generation through a primary 2e− ORR. It is found that the ORR selectivity of M-C is correlated to the content and type of oxygen-containing functional groups in the catalysts, and C-O-C is likely an effective active site for 4e− ORR based on both experimental results and theoretical calculations.